This invention relates to a scroll-type positive displacement machine, and more particularly, it relates to a scroll-type compressor which is equipped with a novel thrust bearing and which is suitable for use as a compressor for an air conditioner or refrigeration apparatus.
A scroll-type compressor is a positive displacement rotary compressor comprising two interfitting elements generally referred to as scrolls. Each scroll comprises a disk-shaped end plate and a thin-walled member, generally referred to as a spiral wrap, which projects perpendicularly from one surface of the end plate and curves outwards from the center of the end plate in the shape of an involute or other type of spiral. The two scrolls are disposed with the end plates parallel and the spiral wraps interfitting with one another so as to be in line contact with one another at a plurality of locations. The surfaces of the end plates and the spiral wraps thereby define a plurality of spiral compression chambers between the locations of line contact between the spiral wraps. If the scrolls are rotated with respect to one another in the proper direction while maintaining the line contact between the spiral wraps, the compression chambers are gradually moved towards the centers of the scrolls with an accompanying decrease in volume. A working fluid is introduced into the compression chambers via a suction port formed in the outer periphery of one of the scrolls and is then removed at a higher pressure from a discharge port formed in the center of the end plate of one of the scrolls.
FIG. 1 is a vertical cross-sectional view of a conventional completely-enclosed scroll-type compressor of the type to which the present invention pertains. The illustrated compressor is like that disclosed in Japanese Laid-Open Patent Application No. 58-117380 and is designed for use as part of a refrigeration apparatus. As shown in this figure, a stationary scroll 1 and an orbiting scroll 2 are housed with a hermetically-sealed shell 12. The stationary scroll 1 has a disk-shaped end plate 1a on the bottom side of which a perpendicularly-extending spiral wrap 1b is formed. The spiral wrap 1b has the transverse cross-sectional shape of an involute. Two diametrically-opposed suction ports 3 are formed in the outer periphery of the spiral wrap 1b of the stationary scroll 1. A discharge port 4 which extends between the top and bottom sides of the end plate 1a is formed at the center thereof. The discharge port 4 is connected to a discharge pipe 17 which penetrates the top of the sealed shell 12.
Likewise, the orbiting scroll 2 comprises a disk-shaped end plate 2a and a spiral wrap 2b which is formed on and extends perpendicularly from the top side of the end plate 2a. The spiral wrap 2b has the same transverse cross-sectional shape as the spiral wrap 1b of the stationary scroll 1, and it interfits with the stationary spiral wrap 1b so as to form a plurality of spiral compression chambers 5 which extend partway around the centers of the scrolls. A short shaft 2c is formed on the bottom surface of the end plate 2a and extends perpendicularly from the center thereof. The moving end plate 2a is eccentric with respect to the stationary end plate 1a.
The stationary scroll 1 is secured by unillustrated bolts to an upper bearing frame 8 which is secured to the inner surface of the sealed shell 12 by press fitting, shrink fitting, or other suitable method. The upper bearing frame 8 has a circular depression 8a formed at the center of its upper surface, and a step 8b which is raised slightly above the rest of the depression 8a is formed at the center thereof. A longitudinally-extending through hole is formed at the center of the frame 8. The depression 8a houses an upper thrust bearing 21 which bears the weight of the orbiting scroll 2 and an Oldham coupling 13. The upper thrust bearing 21 sits atop the step 8b, while the Oldham coupling is supported by the bottom of the depression 8a to the outside of the step 8b. The upper thrust bearing 21 is an annulus whose outer diameter is slightly smaller than the diameter of the depression 8a so that there is a small gap between the outer periphery of the upper thrust bearing 21 and the inner walls of the depression 8a. The Oldham coupling 13 has a pair of keys 13a which slidingly engage with corresponding grooves formed in the bottom side of the moving end plate 2a. The Oldham coupling 13 enables the orbiting scroll 2 to orbit around the center of the stationary scroll 1 without rotating on its own axis. A number of longitudinally-extending oil return holes 25 are formed in the upper bearing frame 8 between the depression 8a and the bottom surface of the upper bearing frame 8, and a longitudinally-extending suction passageway 28 is formed in its outer periphery, the upper end of the suction passageway 28 communicating with the suction ports 3.
A lower bearing frame 8 is disposed immediately below the upper bearing frame 8 and is secured to the inner surface of the sealed shell 12. The two bearing frames 8 and 9 are secured to one another by a faucet joint. The lower bearing frame 9 has a hole at its center through which a drive shaft 6 extends. The drive shaft 6 has a large-diameter portion 6a formed at its upper end, below which a counterweight 6d is formed. The weight of the drive shaft 6 and axial loads are carried by a lower thrust bearing 22 which is formed on the upper surface of the lower bearing frame 9. The large-diameter portion 6a of the drive shaft 6 is journalled by an upper journal bearing 19 which is secured to the inside of the hole at the center of the upper bearing frame 8, while the midportion of the drive shaft 6 is journalled by a lower journal bearing 20 which is secured to the inner surface of the hole at the center of the lower bearing frame 9. A longitudinally-extending eccentric hole 6b is formed in the top of the large-diameter portion 6a, and the shaft 2c of the orbiting scroll is journalled by a moving journal bearing 18 which fits tightly into the eccentric hole 6b. An oil supply hole 6c in the form of a longitudinally-extending, eccentric through hole is formed in the drive shaft 6 between the bottom end of the drive shaft 6 and the bottom end of the eccentric hole 6b. The lower end of the drive shaft 6 has an oil cup 7 having an inlet port 7a fitted thereon. The oil cup 7 is immersed in lubricating oil 15 which fills the bottom of the sealed shell 12. A longitudinally-extending suction passageway 28 is formed in the outer periphery of the lower bearing frame 9. Its lower end opens onto the inside of the sealed shell 12 while its upper end communicates with suction passageway 28 in the upper bearing frame 8. A plurality of oil return passageways 26 are also formed in the outer periphery of the lower bearing frame 9 between its top and bottom sides.
The drive shaft 6 is rotated by an electric motor comprising a rotor 10 which is coaxially mounted on the lower end of the drive shaft 6, and a stator 11 which is secured to the lower bearing frame 9. A plurality of suction passageways 27 are formed in the inner surface of the lower bearing frame 9 to enable working fluid to flow between the lower bearing frame 9 and the stator 11.
A working fluid to be compressed is introduced through a suction pipe 16 which is mounted on the outside of the sealed shell 12 and communicates with a cavity 9a formed in the underside of the lower bearing frame 9 above the motor. As shown by the solid arrows in FIG. 1, the working fluid flows from the suction pipe 16 into the cavity 9a of the lower bearing frame 9. Some of the working fluid flows down the entire length of the motor, while the rest flows through the suction passageways 27 in the lower bearing frame 9. The working fluid then flows upwards through the suction passageways 28 in the bearing frames 8 and 9 and then enters the scrolls through the suction ports 3.
The operation of the illustrated compressor is as follows. When the drive shaft 6 is rotated by the motor, the orbiting scroll 2 is made to orbit around the center of the stationary scroll 1 while being prevented from rotating on its axis by the Oldham coupling 13. Working fluid, shown by the solid arrows, is drawn into the sealed shell 12 through the suction pipe 16, and after cooling the motor windings, it enters the compression chambers 5 formed between the two scrolls via the suction passageways 28 and the suction ports 3. As the orbiting scroll 2 orbits about the center of the stationary scroll 1, the compression chambers 5 are progressively moved around the center of the stationary scroll 1, and as they are moved they decrease in volume, thereby compressing the working fluid. When the working fluid reaches the center of the stationary scroll 1, it is discharged under pressure through the discharge port 4 and the discharge pipe 17 to a high-pressure portion of the refrigeration apparatus of which the compressor is a part.
At the same time, the rotation of the drive shaft 6 causes lubricating oil 15 to be drawn upwards from the bottom of the sealed shell 12 through the oil supply hole 6c. As shown by the dashed arrows in FIG. 1, the lubricating oil 15 is supplied to the upper thrust bearing 21 and the Oldham coupling 13 by way of the eccentric hole 6b in the drive shaft 6. The oil 15 then returns to the bottom of the sealed shell 12 via oil return holes 25 and 26 formed in the bearing frames.
FIGS. 2 and 3 are respectively a plan view and a vertical cross-sectional view of a typical upper thrust bearing 21 for a compressor like that shown in FIG. 1. It is in the form of an annulus and generally has a two-layer structure comprising a bearing layer 21a made of an aluminum alloy, polytetrafluoroethylene, or other suitable bearing material, and a metal backing 21b which is made of rolled steel plate and is secured to the bearing layer 21a by contact bonding or other suitable method. The bearing layer 21a has a plurality of radially-extending grooves 21c formed therein which extend between the hole at the center of the bearing 21 and an annular groove 21d which is concentric with the hole at the center of the bearing 21. A plurality of oil return holes 21e are formed in the annular groove 21d at equal intervals, and a pair of diametrically-opposed notches 21f for the keys 13a of the Oldham coupling 13 are formed in the outer portion of the bearing 21 on the outside of the annular groove 21d. These notches 21f are provided so that the bearing 21 will not interfere with the movement of the Oldham coupling 13. Lubricating oil 15 which is pumped into the eccentric hole 6b of the drive shaft 6 via the oil supply hole 6c flows from the central hole of the upper thrust bearing 21 into the radially-extending grooves 21c, the annular groove 21d, and the oil return holes 21e. In doing so, it lubricates the upper surface of the bearing 21 and the lower surface of the end plate 2a of the orbiting scroll 2.
The lubricating oil 15 flows from the oil return holes 21e into the depression 8a of the upper bearing frame 8. As shown in FIG. 1, there is only a small gap between the outer periphery of the thrust bearing 21 and the inner wall of the depression 8a. Accordingly, most of the oil which enters the depression 8a through the oil return holes 21e returns to the bottom of the sealed shell 12 via oil return holes 25 and 26 formed in the bearing frames 8 and 9. However, due to the presence of the notches 21f for the keys 13a of the Oldham coupling 13 in the outer periphery of the upper thrust bearing 21, it is impossible to completely isolate the bottom portion of the depression 8a from the suction port 3 of the stationary scroll 1. Furthermore, although the gap between the outer periphery of the upper thrust bearing 21 and the depression 8a is small, due to the difficulty of machining a large thrust bearing 21 to high tolerances, the gap is still large enough to allow a significant amount of lubricating oil to leak through it. Accordingly, an undesirably large amount of the oil which enters the depression 8a via the upper thrust bearing 21 is sucked into the compression chambers 5 via the suction ports 3 and is discharged from the compressor together with working fluid.
Furthermore, as shown in FIG. 2, the size of the thrust bearing 21 is larger than is required for it to support the orbiting scroll 2, and it is therefore unnecessarily expensive to manufacture.